http://en.wikipedia.org/wiki/Military_uniform
The regular thematic (provincial) and Tagmata (central) troops of the
Byzantine Empire (East Roman) are the first known soldiers to have had what
would now be considered regimental or unit identification.
不晓得为什么这里会用现在完成式

强调"到目前为止"被认为是....？(不确定)

Because the troops have had that identification for awhile如果改用过去式最好要加上时间抱歉,解释上应该是had had,因为这军队应该已不存在